The present invention is a process for preparing silanes by the reaction of solid silicon monoxide with aromatic halides, in the presence of a catalyst. The described catalysts can increase conversion of the silicon monoxide and alter the product selectivity of the described processes. Product selectivity can be further altered by an activation step comprising the heating of the solid silicon monoxide in an inert atmosphere.
Silanes are primarily produced by the direct reaction of silicon metal with organic halides or hydrogen halides, as first disclosed by Rochow and his co-workers in the 1940's. A significant portion of the cost of this process is the cost of the silicon metal used as a feed material. Silicon metal is typically produced in an electric-arc furnace by the carbothermic reduction of silicon dioxide. This process requires high temperature and high energy consumption, which is reflected in the cost of silicon metal.
Silicon monoxide can be produced at a lower temperature than silicon and, thus, may serve as a less expensive raw material for the production of silanes. The instant invention describes a process whereby potentially less expensive solid silicon monoxide can be reacted with aromatic halides to produce silanes, especially arylsilanes.
Schaschel, in a series of patents, describes a process for preparing organosilicon polymers by reacting silicon monoxide with organic compounds. The methods of the described invention involved preparation of silicon monoxide vapors from solid silicon monoxide by heating the same under vacuum to about 1200.degree. C. to 1300.degree. C.; mixing in a chamber having cooled walls the gaseous silicon monoxide formed thereby, with an excess of a volatile organic compound to form a mixture; and condensing the mixture to obtain the organosilicon polymer. The reaction is reported to occur on the cold surface of the chamber to form the polymer thereupon.
The reactions of organic compounds taught by Schaschel are: Schaschel, U.S. Pat. No. 3,660,448, issued May 2, 1972, organic compounds containing active hydrogen atoms such as alcohols and amines; Schaschel, U.S. Pat. No. 3,660,449, issued May 2, 1972, organic compounds containing a triple bond such as acetylene; Schaschel, U.S. Pat. No. 3,660,451, issued May 2, 1972, organic monohalides such as 1-bromobutane; and Schaschel, U.S. Pat. No. 3,661,961, issued May 9, 1972, aliphatic hydrocarbons such as n-octane.
Timms, U.S. Pat. No. 3,660,450, issued May 2, 1972, teaches a process for reacting gaseous silicon monoxide with an aromatic compound containing at least one benzene nucleus, the compound having no triple bonds and no active hydrogen atoms. The described process is similar to that previously described for the Schaschel series of patents.
Gomberg, U.S. Pat. No. 4,585,646, issued Apr. 29, 1986, teaches a process where Si.sub.2 OCl.sub.6 is irradiated to form solid SiO. The solid SiO is isolated and reacted at 500.degree. C. with HCl. The process is reported to form tetrachlorosilane, water, and hydrogen gas. No SiH-- products are produced. In addition, no activation process for the silicon monoxide or use of a catalyst is taught.
Kuivila et al., Co-Pending U.S. patent application Ser. No. 567,576, filed Aug. 15, 1990, discloses a process for preparing silanes and halosilanes from the reaction of solid silicon monoxide with hydrogen halides. Higher conversion of silicon monoxide to product silanes and altered distribution of the types of silanes produced are observed when the solid silicon monoxide is heat activated in an inert atmosphere prior to contact with the hydrogen halides. Conversion of silicon monoxide and selectivity for the type of silanes produced is also affected when a metal or metal salt catalyst is present during the reaction of unactivated or activated silicon monoxide.
Kuivila et al., Co-Pending U.S. patent application Ser. No. 576,908, filed Sep. 4, 1990, discloses a process for producing silane products from reaction of solid silicon monoxide with alkyl- and alkenyl-substituted halides. The solid silicon monoxide is reacted with the organic halide in the presence of a catalyst which can increase the conversion of silicon monoxide to silanes and partially select for the type of silanes produced. The process may employ an activation step in which the solid silicon monoxide is activated by heating in an inert atmosphere. Activation of the silicon monoxide was found to increase silicon conversion and alter the type of silanes produced.